The Facebook CEO was back before Congress after a marathon five-hour testimony Tuesday afternoon.

The Cambridge Analytica scandal isn't just business for Facebook CEO Mark Zuckerberg. It's also personal.

Zuckerberg is one of the up to 87 million Facebook users whose data was leaked to Cambridge Analytica for use in swaying voter sentiment during the U.S. presidential election, the tech executive revealed Wednesday during his second day of congressional testimony.

During some of the most contentious questioning of the day, Rep. Anna Eshoo grilled Zuckerberg about whether he would change Facebook's business model to protect user privacy. When she wasn't satisfied with his answer, she asked whether his data had been shared with Cambridge Analytica. "Yes," he responded.

Zuckerberg has been in Washington, D.C., this week to take responsibility for the company's handling of private user data. On Tuesday, Zuckerberg sat for a marathon five-hour testimony before two Senate committees. His appearance before the House Energy and Commerce Committee also lasted five hours, with some 50-plus congressmen and congresswomen given four minutes each to grill him on all manner of topics.

Congress has long wanted to compel the billionaire entrepreneur to testify, but he has typically sent deputies. His appearance became all but inevitable after news reports revealed that Cambridge Analytica, a data company with ties to President Donald Trump's 2016 campaign, had obtained the private data of millions of Facebook users that was used to sway voter sentiment.

The first question lobbed at Zuckerberg on Wednesday was about whether Facebook is a media company. Rep. Greg Walden, chairman of the House Energy and Commerce Committee, dove right into questioning just how broad the social networking company's business has become since Zuckerberg started Facebook as a site for connecting with friends in his college dorm room. Citing a recent Facebook series about Patriots quarterback Tom Brady, Walden asked directly, "Is Facebook a media company?"

Zuckerberg responded by noting that Facebook produces enterprise software but doesn't consider itself an enterprise software company, and it builds planes but doesn't consider itself an aerospace company. But he added that the question Facebook has begun to ask is, "Do we have a responsibility to the content that people share on Facebook? And I believe the answer is yes."

Content came up again later in the testimony when Rep. Cathy McMorris Rodgers asked if Facebook "has the unique responsibility that it has clear standards regarding the censorship of content on its platform?" Zuckerberg responded by noting that he's "worried we're not doing a good enough job" of outlining its content policies and standards, especially as it relates to different social norms around the world. He called the issue "one of the more important things that we will do."

Zuckerberg also fielded questions from Rep. G.K. Butterfield, who pushed the company on diversity, noting that all of the five leaders listed on the Facebook website are white. Asked if Facebook would convene a meeting of top technology leaders to address the issue of diversity in Silicon Valley, Zuckerberg said, "We will certainly work with you. This is an important issue." He did not offer specific details about how Facebook would improve diversity within the company.

The big-screen movie about Facebook, The Social Network, also came up in testimony when Rep. Billy Long asked Zuckerberg about Facemash.com, the website Zuckerberg created in 2003 that ranked women based on their appearance. Zuckerberg called the site a "prank website" and confirmed it is no longer up and running. "There was a movie about this, or it said it was about this, it was of unclear truth," Zuckerberg responded, referencing the film, "that claimed that Facemash was somehow connected to the development of Facebook. It isn't. It wasn't."

The questions were often repetitive and regularly required Zuckerberg to explain basic functions about Facebook, which served to showcase just how complex the company's business can be to people outside Silicon Valley.

Among the topics that came up frequently were Facebook's privacy controls, how the company handles the censoring of terrorist-related content and a right-wing show called Diamond and Silk. Hosted by two sisters from North California, the show streams live on Facebook and Twitter and regularly voices support for Trump. The sisters have claimed that Facebook censored their page. On Wednesday, Zuckerberg responded to multiple questions voicing concern over the apparent act of partisanship by saying, "In that specific case, our team made an enforcement error and we have already gotten in touch with them to reverse it."

Meanwhile, Rep. Jeff Duncan used his four minutes to read the First Amendment to Zuckerberg.

Not long before Zuckerberg began his second day of Congressional testimony, the social network's shares opened up for the day on the Nasdaq, a signal that investors were feeling good about the billionaire founder's first day in the hot seat. By the time he took the stand before the House Committee on Energy and Commerce, the stock was trading down slightly at around $164 per share. They closed the day basically flat (up $1.28) at $166.32.